The objective of the proposed work is to define and characterize those surface-associated, or cell-bound, factors which contribute to the virulence of enteropathogenic Escherichia coli, including enterotoxigenic E. coli (ETEC) and the classical enteropathogenic E. coli serogroups (EPEC). The primary event in bacterial secretory diarrhea is attachment of the bacteria to the epithelial cell surface of the intestinal mucosa via specific structures on the surface of the bacteria. These are usually, but not necessarily, in the form of fimbriae, otherwise called pili. Following adhesion, bacterial multiplication results in gross colonization of the mucosal surface with subsequent production of enterotoxic substances. This investigator and coworkers have discovered and partially characterized two major colonization factor antigens of ETEC. These are CFA/I and CFA/II which are produced by different serotypes of ETEC. These studies will be extended to include the EPEC. Preliminary work has determined that the CFAs of ETEC are mannose-resistant hemagglutinins (MRHAs) and that enteropathogenic E. coli other than ETEC also produce MRHAs which relate to virulence but these are antigenically different. These results need to be confirmed and extended. The mechanism of pathogenesis of EPEC is not understood except that these cause enteritis in infants and young children. This investigator and others have found that mannose-sensitive hemagglutinins (MSHAs) of E. coli also contribute to the virulence of E. coli. These antigens are more heterogeneous than originally thought and antigenic analyses of the MSHAs of virulent and avirulent isolates will be carried out, as well as tests for virulence using in vivo models and tissue culture systems which measure adhesiveness of bacteria to human intestinal epithelial, and other types of cells. Techniques will be employed to assay EPEC isolates for the ability to survive in mammalian cells and tissue.